From: Paul E. McKenney Date: Mon, 4 Nov 2019 16:22:45 +0000 (-0800) Subject: rcu: Use READ_ONCE() for ->expmask in rcu_read_unlock_special() X-Git-Tag: v5.5.3~332 X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=09d89628a6d711d3887bdc599b556081443a4dd9;p=users%2Fdwmw2%2Flinux.git rcu: Use READ_ONCE() for ->expmask in rcu_read_unlock_special() commit c51f83c315c392d9776c33eb16a2fe1349d65c7f upstream. The rcu_node structure's ->expmask field is updated only when holding the ->lock, but is also accessed locklessly. This means that all ->expmask updates must use WRITE_ONCE() and all reads carried out without holding ->lock must use READ_ONCE(). This commit therefore changes the lockless ->expmask read in rcu_read_unlock_special() to use READ_ONCE(). Reported-by: syzbot+99f4ddade3c22ab0cf23@syzkaller.appspotmail.com Signed-off-by: Paul E. McKenney Acked-by: Marco Elver Signed-off-by: Greg Kroah-Hartman --- diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 270779418a607..f849e7429816f 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -612,7 +612,7 @@ static void rcu_read_unlock_special(struct task_struct *t) t->rcu_read_unlock_special.b.exp_hint = false; exp = (t->rcu_blocked_node && t->rcu_blocked_node->exp_tasks) || - (rdp->grpmask & rnp->expmask) || + (rdp->grpmask & READ_ONCE(rnp->expmask)) || tick_nohz_full_cpu(rdp->cpu); // Need to defer quiescent state until everything is enabled. if (irqs_were_disabled && use_softirq &&